1. Field of the Invention
The present invention relates to magnetic separation apparatuses and magnetic separation methods, and wastewater treatment apparatuses and wastewater treatment methods and, in particular, to a magnetic separation apparatus and a magnetic separation method, and a wastewater treatment apparatus and a wastewater treatment method that separate suspended solids, oil, and heavy metals from wastewater containing the suspended solids, the oil, and the heavy metals to thereby obtain treated water.
2. Description of the Related Art
Conventionally, wastewater treatment apparatuses using magnetic separation apparatuses have been known for separating suspended solids, oil, and heavy metals from wastewater containing the suspended solids, the oil, and the heavy metals. In such wastewater treatment apparatus, magnetic powder is added to the wastewater when suspended solids, oil, and heavy metals that are contained in wastewater are flocculation-treated, and flocculation flocs (hereinafter referred to as magnetic flocs) containing the magnetic powder are separated with magnetic force of a magnetic separation apparatus to thereby obtain treated water.
FIG. 10 is a block diagram showing a configuration of a wastewater treatment apparatus 100 disclosed in Japanese Patent Application Laid-Open No. 2009-112978.
In this wastewater treatment apparatus 100, wastewater is mixed with a polymeric flocculant in a slow stirring tank 104 after being mixed with magnetic powder (for example, ferrosoferric oxide) and an inorganic flocculant (for example, ferric chloride or polyaluminum chloride) in a rapid stirring tank 102. Suspended solids, oil, heavy metals, etc. in the wastewater are taken into magnetic flocs generated in the rapid stirring tank 102 and the slow stirring tank 104, and thereby the wastewater is purified. The magnetic flocs are separated by a floc separation apparatus 106 installed at a subsequent stage of the slow stirring tank 104. The floc separation apparatus 106 is composed of a magnetic separation apparatus 108 and a filter 110. Wastewater from which the magnetic flocs have been separated results in treated water. The magnetic flocs that have not been separated by the magnetic separation apparatus 108 are separated and removed by the filter 110 in the subsequent stage, and are again returned to the magnetic separation apparatus 108 to be separated.
However, the wastewater treatment apparatus 100 disclosed in Japanese Patent Application Laid-Open No. 2009-112978 has a problem that although clear treated water can be obtained by the magnetic separation apparatus 108 and the filter 110 installed side by side, continuous reverse cleaning that requires a larger filtration area is needed in order to prevent clogging of the filter 110. Namely, although the wastewater treatment apparatus 100 disclosed in Japanese Patent Application Laid-Open No. 2009-112978 has an advantage that a footprint thereof can be made dramatically smaller by using the magnetic separation apparatus 108 instead of a sedimentation basin, the advantage of the magnetic separation apparatus 108 has been impaired because of the requirement of the large filter 110.
Meanwhile, there will be shown a structure of a disk-shaped magnetic separation apparatus 120 disclosed in Japanese Patent Application Laid-Open No. 2009-101339 in FIGS. 11 and 12. It is to be noted that FIG. 11 is a plan view of the magnetic separation apparatus 120, and FIG. 12 is an elevational view thereof, which are perspective explanatory views of a cross section of a semicircular separation tank 122.
Disks 124 and 126 having magnetic force are arranged at a predetermined interval in this separation tank 122 of the magnetic separation apparatus 120. A shaft 128 is fixed to centers of these disks 124 and 126, and is connected to a motor (not shown). The disks 124 and 126 are rotated in a counterclockwise direction as shown in FIG. 12 through the shaft 128 by this motor. In addition, height positions of the disks 124 and 126 have been set so that lower halves thereof may be under wastewater when it flows into the separation tank 122.
A supply portion 130 of wastewater is provided at a bottom center of the separation tank 122. Consequently, flocculated wastewater flows into in the separation tank 122 as an upward flow from the supply portion 130, and it branches in two directions as the supply portion 130 being a center thereof. Subsequently, while the wastewater flows toward treated water outlets 132 and 134 provided at both sides of a top of the separation tank 122, magnetic flocs in the wastewater adhere to the disks 124 and 126. In addition, the magnetic flocs having adhered to the disks 124 and 126 are scraped by a scraper 136 provided between the disks 124 and 126 at a time of rotation thereof. The scraped magnetic flocs are then scraped by a sludge scraper 138 provided along the scraper 136, and discharged to an outside of the magnetic separation apparatus 120.
In this magnetic separation apparatus 120, there exists a region where a water flow direction in the separation tank 122 and a rotational direction of the disks 124 and 126 become opposite to each other (a left side portion as viewed from the shaft 128 shown in FIG. 12). In this region, since a force of detaching the magnetic flocs having adhered to the disks 124 and 126 acts largely on the magnetic flocs due to a flow of wastewater, quality of treated water may slightly deteriorate. Hence, there has been required a filter at a subsequent stage of the treated water outlet 134 in the magnetic separation apparatus 120 disclosed in Japanese Patent Application Laid-Open No. 2009-101339.
As described above, a large filter is needed at a subsequent stage of a magnetic separation apparatus in order to obtain clear treated water in a conventional wastewater treatment apparatus using magnetic force, and thus there has been a disadvantage of impairing an advantage of the magnetic separation apparatus that allows a smaller footprint of the wastewater treatment apparatus.
The present invention is made in view of such circumstances, and has an object of providing a magnetic separation apparatus and a magnetic separation method, and a wastewater treatment apparatus and a wastewater treatment method that allow to obtain clear treated water only with the magnetic separation apparatus without using a filter.